The present invention relates to a new and distinctive sunflower inbred line, designated H1063R. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include improved seed yield, earlier maturity, shorter plant height, uniformity of plant type and disease and insect resistance. High oil percentage is important in breeding oilseed types whereas large seed size, a high kernel-to-hull ratio, and uniformity in seed size, shape, and color are important objectives in breeding and selection of nonoilseed sunflower. Other characteristics such as improved oil quality are also important breeding objectives.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Sunflower (Helianthus annuus L.), can be bred by both self-pollination and cross-pollination techniques. The sunflower head (inflorescence) usually is composed of about 1,000 to 2,000 individual disk flowers joined to a common base (receptacle). The flowers around the circumference are ligulate ray flowers with neither stamens nor pistil. The remaining flowers are hermaphroditic and protandrous disk flowers.
Natural pollination of sunflower occurs when flowering starts with the appearance of a tube partly exerted from the sympetalous corolla. The tube is formed by the five syngenesious anthers, and pollen is released on the inner surface of the tube. The style lengthens rapidly and forces the stigma through the tube. The two lobes of the stigma open outward and are receptive to pollen but out of reach of their own pollen initially. Although this largely prevents self-pollination of individual flowers, flowers are exposed to pollen from other flowers on the same head by insects, wind and gravity.
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 generations from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of plant breeding is to develop new, unique and superior sunflower inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same sunflower traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines which are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new sunflower inbred line.
The development of commercial sunflower hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1's or by intercrossing two F1's (sib mating). Selection of the best individuals is usually begun in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny. A double-cross hybrid is produced from four inbred lines crossed in pairs (A×B and C×D) and then the two F1 hybrids are crossed again (A×B)×(C×D). Much of the hybrid vigor exhibited by F1 hybrids is lost in the next generation (F2). Consequently, seed from hybrid varieties is not used for planting stock.
A reliable method of controlling male fertility in plants offers the opportunity for improved plant breeding. This is especially true for development of sunflower hybrids, which relies upon some sort of male sterility system. Two types of male sterility, genetic and cytoplasmic, have been found in sunflower.
Hybrid sunflower seed is typically produced by a male sterility system incorporating genetic or cytoplasmic male-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile as a result of factors resulting from the cytoplasmic, as opposed to the nuclear, genome. Thus, this characteristic is inherited exclusively through the female parent in sunflower plants, since only the female provides cytoplasm to the fertilized seed. CMS plants are fertilized with pollen from another inbred that is not male-sterile. Pollen from the second inbred may or may not contribute genes that make the hybrid plants male-fertile.
Hybrid sunflower seed is typically produced by a male sterility (CMS) system. Alternate strips of two sunflower inbreds, male and female, are planted in a field. Providing that there is sufficient isolation from sources of foreign sunflower pollen, florets of the female (CMS) inbred will be fertilized only from the other inbred (male). Pollen is typically transferred by bees placed in the field and the resulting seed is therefore hybrid and will form hybrid plants.
Plant breeding methods involving genetic or cytoplasmic male sterility, or induction of male sterility by gibberellic acid, allow for complete hybridization of lines and hence greater precision in estimating combining ability. Various tester parents and tester schemes are being used. A. V. Anaschenko has conducted extensive testing for general combining ability by the top cross method with chemical emasculation of the female parent with gibberellic acid. He has used open pollinated cultivars, hybrids and inbred lines as testers. A. V. Anaschenko, The Initial Material for Sunflower Heterosis Breeding, Proceedings of the 6th International Sunflower Conference, 391-393 (1974). V. Vranceanu used a monogenic male sterile line as a female parent to test for general combining ability and subsequent diallel cross analysis with artificial emasculation to test for specific combining ability. V. Vranceanu, Advances in Sunflower Breeding in Romania, Poc. 4th International Sunflower Conference (Memphis, Tenn.), 136-146 (1970). Recent testing by breeders in the United States has included the rapid conversion of lines to cytoplasmic male sterility by using greenhouses and winter nurseries and subsequent hybrid seed production in isolated crossing blocks using inbred lines as tester.
There are several methods of conferring genetic male sterility available, such as multiple mutant genes at separate locations within the genome that confer male sterility. According to A. I. Gundaev, Prospects of Selection in Sunflower for Heterosis, Sb. Rab. Maslichn. Kult., 3:15-21 (1966), genetic male sterility first was reported in the Soviet Union by Kuptsov in 1934. Since then, numerous investigators have reported genetic male sterility in sunflower. Vranceanu indicated isolation of more than thirty sources of male sterility in the Romanian program, most of which were controlled by a single recessive gene. Diallel cross analysis of ten of these lines indicated the presence of five different genes. The studies of E. D. Putt and C. B. Heise, Jr. were some of the first reported to assess the value of genetic male sterility to produce hybrid seed. They concluded that the lines of partial male sterility may have the most immediate value in commercial production of hybrid seed as not only could the partial male sterile lines hybridize well in crossing plots, they could also be increased and easily maintained. E. D. Putt and C. B. Heiser, Jr., Male Sterility and Partial Male Sterility in Sunflowers, Crop Science, 6:165-168 (1966).
In order to produce hybrid seed using complete genetic male sterility, the male sterile locus must be maintained in the heterozygous condition in the female parent. This is accomplished by sib pollinations of male sterile plants (ms ms) with heterozygous male fertile plants (Ms ms) within the female parent. The resultant progeny from the male sterile plants will segregate 1:1 for fertile and sterile plants. When such lines are used in hybrid seed production the fertile plants must be removed prior to flowering to obtain 100% hybridization with the male parent line.
The laborious, and occasionally unreliable, genetic male sterility system can be avoided by using cytoplasmic male-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile as a result of factors resulting from the cytoplasmic, as opposed to the nuclear, genome. Thus, this characteristic is inherited exclusively through the female parent in sunflower plants, since only the female provides cytoplasm to the fertilized seed. CMS plants are fertilized with pollen from another inbred that is not male-sterile. Pollen from the second inbred may or may not contribute genes that make the hybrid plants male-fertile.
Cytoplasmic male sterile lines are traditionally developed by the backcrossing method in which desirable lines that have undergone inbreeding and selection for several generations are crossed initially to a plant with cytoplasmic male sterility. Thereafter the inbred line to be converted is used as a recurrent parent in the backcrossing procedure. The final progeny will be genetically similar to the recurrent parent except that it will be male sterile.
Fertility restorer lines are developed by transferring a dominant restorer gene to an established inbred line with normal cytoplasm by backcrossing. If this procedure is used, selected plants must be crossed to a cytoplasmic male sterile line after each generation to determine if the fertility restorer genes are present. A more common procedure is self-pollination and selection of male fertile plants from commercial hybrids or planned crosses of parents having restorer genes in male sterile cytoplasm. This procedure does not require test crossing to a male sterile line during selection because the plants will be fully male fertile if the necessary restoring genes are present.
Typically most fertility-restorer lines in use today have restorer genes in male sterile cytoplasm, are resistant to older races of downy mildew and have recessive branching. The later trait extends the period of pollen production and is useful in obtaining simultaneous flowering with female lines in hybrid seed production fields. Restorer lines RHA271, RHA273, and RHA274 were the first such lines to be developed and have been used widely in producing hybrids in breeding programs throughout the world.
Other methods for conferring male sterility are also available and could be used in developing male sterile and fertility restoring sunflowers. For example, Albertsen et al., of Pioneer Hi-Bred, have developed a system of nuclear male sterility in corn which could also be used in sunflower which includes: identifying a gene which is critical to male fertility; silencing this native gene which is critical to male fertility; removing the native promoter from the essential male fertility gene and replacing it with an inducible promoter; inserting this genetically engineered gene back into the plant; and thus creating a plant that is male sterile because the inducible promoter is not “on” resulting in the male fertility gene not being transcribed. Fertility is restored by inducing, or turning “on”, the promoter, which in turn allows the gene that confers male fertility to be transcribed.
There are many other methods of conferring male sterility in the art of the plant breeding and any method can be used, each with its own benefits and drawbacks. These methods use a variety of approaches such as delivering into the plant a gene encoding a cytotoxic substance associated with a male tissue specific promoter or an antisense system in which a gene critical to fertility is identified and an antisense to that gene is inserted in the plant (see: Fabinjanski, et al., EPO 89/3010153.8 publication number 329,308 and PCT application PCT/CA90/000037 published as WO 90/08828).
There are many other methods of conferring genetic male sterility in the art, each with its own benefits and drawbacks. These methods use a variety of approaches such as delivering into the plant a gene encoding a cytotoxic substance associated with a male tissue specific promoter or an anti-sense system in which a gene critical to fertility is identified and an antisense to that gene is inserted in the plant (see, Fabinjanski, et al. EPO 89/3010153.8 publication no. 329, 308 and PCT application PCT/CA90/00037 published as WO 90/08828).
Another version useful in controlling male sterility makes use of gametocides. Gametocides are not a genetic system, but rather a topical application of chemicals. These chemicals affect cells that are critical to male fertility. The application of these chemicals affects fertility in the plants only for the growing season in which the gametocide is applied (see Carlson, G. R., U.S. Pat. No. 4,936,904). Application of the gametocide, timing of the application and genotype specifically often limit the usefulness of the approach.
Sunflower is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding sunflower hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the sunflower breeder must select and develop sunflower plants that have the traits that result in superior parental lines for producing hybrids.